Or, are there examples in history where leaders took a "liberal" position on an issue with favorable results, or a "conservative" position that turned out badly?

I'd be interested in what the contributors here think about this, so all are invited to respond below.

Yes

By refusing to consider a progressive position, purely on the grounds that "we've never done it that way", scientists or politicians can easily fall into error. For example, it was southern Democrats who opposed racial integration, saying it was "too much too soon".

"Electability?"

One argument might be that, given the current US political system, candidates need to appeal to a broad spectrum of voters which includes liberals and people with liberal tendencies. A candidate who is extremely conservative might have less chance of attracting votes from these people than one who is only quite conservative. Therefore, it might be better from a tactical point of view for conservative candidates in some areas to sacrifice some conservative policies in pursuit of increased "electability". After all, a conservative can make much more of a difference when in office than when in opposition.

No

Conservatism is the best political philosophy, so all the current U.S. conservative positions on the issues are superior to all the liberal positions.